The invention relates to an method for combusting multifarious waste material, as well as a oven to be used thereby. The invention also relates to a universal combustion system with a number of such ovens.
Waste removal is one of the most serious problems of the present time. In order to be able to stand up to the continuously increasing quantities of waste materials, waste is more and more often disposed of by means of combustion. In practice, solid and liquid waste materials are mainly combusted in ovens with a sliding grid or ovens with a rotating drum. In ovens with a sliding grid, waste materials are continuously supplied to a moving grid and air is blown through the burning mass by way of apertures in the grid. The temperature may increase locally to over 1000.degree. C., while elsewhere the temperature may remain below 800.degree. C. Under such conditions much fly-ash is formed, while in the areas where the temperature is too low, unpleasantly smelling substances will remain or be formed by incomplete combustion, which by their unpleasant smell alone will already create a burden for the environment.
In a oven with an rotating drum, waste materials are kept in motion by the slow rotation of the cylindrically shaped oven, under which conditions the advantage is obtained, that the areas of too low a temperature, such as in a oven with a grid, may be avoided. However the temperature for a oven with a rotating drum should not rise much above 1000.degree. C. in order to prevent the deposition fluid slag against the wall. Downstream of an oven with a rotating drum, a chamber for after-burning may be positioned, in which the temperature is increased to, for example, 1150.degree. C. by additional combustion of fuel.
The residence times of gases in hot areas (temperatures of more than 800.degree. C.) of the ovens amount in general to 1 to 3 sec. The incomplete combustion, the relatively low temperature, the short residence times of the compounds in the hot areas, provide the conditions for the formation of many poisonous and unpleasant smelling compounds, such as dioxins and benzofuranes.
As such oven processes are very expensive, it is in general the objective, that the thermal energy created thereby will not get lost, but will be utilized as much as possible for re-use. To that end the hot combustion gases created, are passed into a steam-boiler in order to utilize the energy of the gases for generating steam. Thereby the gases will gradually cool down to about 200.degree. C. As a consequence of this gradual cooling down dioxins, which are detrimental to the environment, may be created.